flipside, n. — Green’s Dictionary of Slang

flipside n.

[rock music use, the ‘other side’ of a record, the B-side]

1. the reverse, the alternative.

1968		Time 4 Oct. 63: Barbra [Streisand] [...] is the flip side of cinderella — the homely girl who made it.
1977		C. McFadden Serial 88: Anger is just the flip side of depression.
1999		K. Sampson Powder 39: But there was a flipside. If you failed to send out the letter of love to twenty people within ninety-six hours you were fucked.
2009		L. Tye Satchel 296: If drilling lessons into his kids was Satchel’s stiff and proper side, his flip side was soft as custard.

2. (US gay) the anus; the buttocks [the man ‘flips over’ to offer his anus for sex].

on the flipside

(also on the flip) on the other side, on the reverse, ‘on the other hand’.

1992		D. Burke Street Talk 2 180: If our plan suceeds, we could earn thousands of dollars. On the flip side, if we fail, we could lose everything.
2003		Guardian 17 Feb. 🌐 The Sultan of Sokoto appealed for calm and peace. On the flip side, the minister for Abuja, Nigeria’s glossy capital, broke down in front of the camera, weeping that I had blasphemed the prophet.
2007		D. McDonald Luck in the Greater West (2008) 5: Credit could be obtained, but terms were very short. On the flipside though [...] there was no interest.
2012		J.J. DeCeglie ‘Death Cannot Be Delegated’ in Crime Factory: Hard Labour [ebook] On the flip nothing made you feel more intense [...] Not a thing.
2021		T. Pluck Boy from County Hell 341: ‘Catch you on the flip side’.